But experiments suggest the superworms make the metals easier for plants to extract from the soil, Hodson said.

"The earthworms don't necessarily render the metals less toxic, but they do seem to make them available for plant uptake," he said. This raises this possibility of using the earthworms as part of efforts to clean up land contaminated by mining and heavy industry.

The long-term aim is to breed and then release the worms at polluted sites to speed up the process of soil development and help kick-start the ecosystem's rehabilitation, Hodson said.

Plants could be used to extract toxic metals once the superworms have got to work, he added.

This in turn could boost the development of methods for using plants to mine metals.

"The goal at the end of the rainbow is that the plants become so efficient at it that you can use them as a source of metal in industrial processes," Hodson said. "So you just crop off the plants and take them to a processing plant."

Peter Kille of the School of Biosciences at Cardiff University in Wales has also been tracking the metal-eating worms.

He said previous studies show it takes earthworms many years to improve polluted soils. While the new superworms should prove a useful tool, even they can't compete with industrial cleanup processes that take one to two years.

The worms, however, are an excellent way to diagnose metal concentrations in contaminated land, Kille said.

"Basically you can see the earthworms as biological dipsticks of the soil toxicity and the metal levels," he said.

And the superworms are perfect subjects for studying evolution in action, Kille added.

"What's really interesting is that each patch of high metal creates a unique evolutionary event," he said. The worms either develop new ways of dealing with the metals or find solutions similar to other populations.

"Each time it happens it's a localized event, and it allows us to study the processes of evolution that create the adaptation," he said.